With such a cutting tool, the or each cutting insert is releasably retained in a respective pocket formed in a tool holder by, for example, a clamping screw which extends through a central hole formed in the insert into an appropriate tapped bore formed in the tool holder or, alternatively, by some other suitable clamping system. In many cases, a metal shim is interposed between the insert and the bottom wall of the tool holder pocket, this shim serving to protect the tool holder proper from excessive wear or damage through use. Additionally, shims of differing heights can be employed so as to vary as required the specific location of the cutting insert with respect to the tool holder and in particular that of the cutting edge. In most cases where such shims are employed with screw bolted inserts, the shim is retained in position in the pocket by means of the same screw used to secure the insert, which screw passes through an aperture formed in the shim aligned with the bore of the insert. It will be readily appreciated that this method of securing the shim to the tool holder is inconvenient, particularly in view of the fact that during replacement of an insert, the shim is no longer secured to the holder and can either become lost or forgotten when the operator may forget to replace the shim.
In order to overcome this problem, and also to ensure that the shim is effectively secured to the tool holder even when the insert is retained by means other than a through-going bolt, it has been proposed, particularly in connection with milling tools, to retain the shim in position with respect to the tool holder quite independently of the releasable retention of the insert, and this by means of a special retaining pin which is inserted into the tool holder and retains the shim in position. It has been found in practice, however, that the retaining pin often becomes broken and this in itself can have undesirable consequences in the use of the cutting tool. Additionally, with shims so retained, difficulties are often encountered in releasing the shim for replacement and such replacement may become time consuming.